It has been said that the miniaturization of electronic devices has revolutionized the technology of today, while the miniaturization of mechanical devices will revolutionize the technology of the future. Nanoelectromechanical systems (NEMS) with molecular-scale components operating at ultrahigh (microwave) frequencies promise applications ranging from single-atom mass and force sensing to efficient energy conversion systems to quantum computation. Despite recent nanotechnology advances facilitating the construction of very small-scale devices, a seemingly insurmountable barrier has been the realization of practical (i.e., operating at room temperature in atmospheric pressure) ultrahigh frequency mechanical oscillators. The challenge is two-fold: materials must be fabricated with nanoscale dimensions and with relatively defect-free surfaces, and detection methods with suitable sensitivity to the ultra-small displacements must be employed.
Exemplified below are the construction and operation of nanotube-based “nano-abacus” devices functioning as self-detecting NEMS oscillators, capable of operating in ambient-pressure air at room temperature with fundamental resonance frequency near 4 GHz. Such devices are referred to as “abacus” devices because they can, in one embodiment, take the form of moveable beads on a wire. Specialized nonlinear mixing methods are used to detect the resonance. The devices are individually tunable post-production and suitable for practical microwave frequency NEMS applications.
U.S. Pat. No. 4,137,511 to Jones, issued Jan. 30, 1979, entitled “Electromechanical filter and resonator,” describes an electromechanical filter or resonator in the form of a single planar body comprises an elongated torsionally vibrating member, and a flexurally vibrating resonating element coupled along its nodal axis to the member. A pair of electromechanical transducers is attached to at least one side of the resonating element for exciting and/or detecting mechanical vibrations in the filter or resonator. Mounting sections located at both ends of the member are used to attach the filter or resonator to a base.
U.S. Pat. No. 6,803,840 to Hunt, et al., issued Oct. 12, 2004, entitled “Pattern-aligned carbon nanotube growth and tunable resonator apparatus,” discloses an oscillator device comprising a suspended nanotube, designed such that injecting charge density into the tube (e.g., by applying a capacitively-coupled voltage bias) changes the resonant frequency of the nanotube, and where exposing the resonator to an RF bias induces oscillatory movement in the suspended portion of the nanotube, forming a nanoscale resonator, as well as a force sensor when operated in an inverse mode.
U.S. Pat. No. 6,756,795 to Hunt, et al., issued Jun. 29, 2004, entitled “Carbon nanobimorph actuator and sensor,” discloses nanomechanical actuator/oscillator device nanotubes, designed such that inducing a difference in charge density between the tubes (e.g., by biasing one tube positive with respect to the other with sufficient tube-to-tube contact resistance) induces lateral movement in the end of the bimorph, forming a nanoscale resonator.
U.S. Pat. No. 6,737,939 to Hoppe, et al., issued May 18, 2004, entitled “Carbon nanotube array RF filter,” discloses a tunable nanomechanical resonator system comprising an array of nanotubes, where the nanotubes are in signal communication with means for inducing a difference in charge density in the nanotube such that the mechanical resonant frequency of the nanotube can be tuned. The nanotube is in signal communication with a waveguide or other RF bias conduit such that an RF signal having a frequency corresponding to the mechanical resonant frequency of the array will couple to the array thereby inducing resonant motion in the array of nanotubes.
US 2006/0057767 to Regan et al., (including a present inventor) published Mar. 16, 2006, entitled “Nanoscale mass conveyors,” discloses a mass transport method and device for individually delivering chargeable atoms or molecules from source particles is disclosed. It comprises a channel; at least one source particle of chargeable material fixed to the surface of the channel at a position along its length; a means of heating the channel; and a means for applying an controllable electric field along the channel, whereby the device transports the atoms or molecules along the channel in response to an applied electric field.
Peng et al., (including the present inventors) “Ultrahigh Frequency Nanotube Resonators,” Phys. Rev. Lett. 97, 087203 (Aug. 27, 2006), describes suspended carbon nanotube (“CNT”)-based resonators with the fundamental mode frequency over 1.3 GHz and mechanical motion self-detectable at room temperature in air at atmospheric pressure. A combination of drive and detection methods, along with metal nanobridges templated onto the CNT beam, are used to dramatically enhance the response sensitivity (including phase response) and to probe mobility of trapped charges of the NEMS device.
Sazonova et al., “A tunable carbon nanotube electromechanical oscillator,” Nature 431, 284-287 (16 Sep. 2004) disclose an oscillator comprising nanotubes (typically single- or few-walled, 1-4 nm in diameter and grown by chemical vapor deposition), which are suspended over a trench (typically 1.2-1.5 μm wide, 500 nm deep) between two metal (Au/Cr) electrodes. A small section of the tube resides on the oxide on both sides of the trench; the adhesion of the nanotube to the oxide provides clamping at the suspension points.
Kong et al., “Synthesis of individual single-walled carbon nanotubes on patterned silicon wafers,” Nature 395:878-881 (29 Oct. 1998) disclose strategy for making high-quality individual SWNTs on silicon wafers patterned with micrometer scale islands of catalytic material.
Knobel et al., “Nanometer-scale displacement sensing using a single electron transistor,” Nature 424, 291-293 (17 Jul. 2003) disclose an oscillator which has a 3 μm long 250 nm wide 200 nm thick doubly-clamped beam of single-crystal GaAs, capacitively coupled to an aluminum SET (single electron transistor), located 250 nm from the beam. The charge sensitivity of the SET at cryogenic temperatures is exploited to measure motion by capacitively coupling it to the mechanical resonator. The device yields a displacement sensitivity of 2×10−15 m Hz−1/2 for a 116-MHz mechanical oscillator at a temperature of 30 mK.
Huang, et al., “Nanoelectromechanical systems: Nanodevice motion at microwave frequencies,” Nature 421, 496 (2003) discloses a nanodevice that will operate with fundamental frequencies in the microwave range (greater than 1 gigahertz). The device used 3C—SiC (silicon carbide) films. Optical and electron-beam lithography was used to define, respectively, large-area contact pads and submicrometer-scale, thin metallic-film masks with the device geometry. Each doubly clamped beam pair is positioned perpendicular to a strong magnetic field (3-8 tesla) in vacuo.